Motor-control system.



G. E. STACK.

MCTCB. CONTROL SYSTEM.

APPLICATION FILED JULY 31, 1912.

l gggg la. Patented Jan. w15.

.s f /09 C/ C TYZTNESSES 72V VEN T01-tl.

EM EEDHGE .'E. E'TCIQ :BY-M

GEORGE El STACK,

OF SCEN'ECTADY, NEW YOBIKSSIGNOB T0 GENERAL ELECTRIC CMPNY, ACDB'PORATION 0l' NEW YORK.

MOTOR-CONTROL SYSTEM.

speci-muon of' Letters 15mm.

Patented Jan. 2e, 1915.

Application'ld July 31, 1912. Serial No. 712,385.

To all 'whom z't may concern:

Be it known that I, GEORGE E.v STACK, a citizen of the United States,residingat Schenectady, in the county of Schenectady,

.State of New York, have invented certain new and'useful Improvements inMotor- Control Systems, of which the following is l a specification.

This invention relates tothe control of electric motors and has for itsobject the provision of means whereby an electric motor may be started,stopped and generally controlled in a reliable, simple and `eiicientmanner.- l

My invention relates more specifically to the control of motors whichare brought to rest by dynamically braking the motor.`

In thecontrol of electric motors it is common to retard the motorarmature by causing. it to generate current through a resistance.Sometimes this is accomplished `by leaving the armature connected to thesupply circuit and causing it to restore energy to the line.` Morefrequently the armature i'sdisconnected from the line and connected to abraking resistance so that the l armature will generate current throughthe resistance, With either method of braking it has been founddesirable to increase the dynamic braking current so as to increase thebraking torque as the armature slows down during braking. lf theresistance in circuit is constant, the current will decrease and'consequently the torque tending to stop the motore. if the brakingcurrent is high i enouglfi to be ettective after the motor has sloweddowngit willl be toc i'ii'gh during the initial braking period and causesparking at the cemmutator' and other troubles.-

-' decreasing the resistance as the motor slows down, the torque may beincreasedl so as to bring the motor to rest more quickly and withoutinjury to the motor and other apparatus due to excessive current How.@ne method which has been suggested is to controlv the dynamic bra-kingcurrent by a relay which depends. for its action upon the ield strengthci the motor".

In carrying out my invention l provide means whereby the' dynamicbraking current will be controlled by the same means which centrols thestarting. resistance. ln one emtmdiment` of my invention, l provide acounter electromotive force relay for controlling the startingresistance and cause this same relay to control the dynamic brak- I ingcurrent. The arrangement is such that as the motor speeds up the relaywill be lifted to short circuit the starting resistance and after .thedynamic brake has been applied and the motor armature has4 slowed downto a predetermined speed, the' relay will drop to short circuit thebraking resistance asa whole or in part.

My invention is particularly applicable to reversible electric motorsfor use on machine tools in which the motor is to be periodicallyreversed, as for instance in planers,y nut tappers, and the like,although itis equally applicable to reversible motors for otherpurposes, as well asto non-reversible motors.

Other objects and purposes oilily, invention will appear in the courseof the following specification in which I have shown my inventionembodied in concrete form for purposes of illustration.

In the accompanying drawing illustrating one form of my invention, Arepresents the armature land F the shunt field of an electric-motor tobe controlled.

R represents the starting resistance for the motor and Cv and Drepresent two electromagnetic switches, one for closing the motorcircuit through the resistancel R or each d1- rection of rotation. Amaster switch S con-I trols these two reversing electromagnetic switchesso that when the switch S is moved into engagement with contact 10 theswitch C will be closed to start the motor through the resistance andwhen it moves into engagement with contact il the switch D w1ll ciose tostart the motor through the resistance it in the' opposite direction.QThe switches C and D have operating windings and 13 respectively formoving the switches to closed position, these windings being connectedin shunt to the motor. In addition to these windings the switches areprovided with series windings 1 4 and 15 for holding the switches inoperative position, as hereinafter described. |lihe switch C is providedwith two switch contacts 16 and 1'?, the former for bridging thecontacts 18 when the switch is in the closed position while the latteroperates to bridge the 'conf ."W switch C completes the armature circuitas is adapted to be connected in short circuit with the motor armatureto retard the motor when both the switches C and D are in their openposition. y

E represents a relay which I have shown as a counter electromotive forcerelay for controlling the motor circuit. This relay performs twofunctions. Durin the starting of the motorv this relay li ts Yitscontact 24 into engagement with the contacts 25 so as to short circuitthe resistance R when the motor reaches a predetermined speed. The relaylalso acts to control the dynamic braking current. The arrangement issuch that when the two switches C and D are open z'. e. in the downposition in which the motor is disconnected from the supply circuit themotor is dynamically braked by and the master switch S is moved intoenthrough resistance gagement with the contact 10, then theelectromagnetic switch C will be closed, the circuit through theenergizing winding 12 being as follows: from the positive side of theline, contact 10 of switch S, winding 12, conductor 27 winding 15,contacts 23, conductor 28, across the contacts 26 of the counterelectromotive force relay and back to the lnegative side of the linethrough the series commutating'iield F. The closure of the ositive sideof the line, contacts 20, winding 14, armature A, conductor 27, winding15, contacts 23, conductor 28, contacts 18 orn follows: from the lswitch C, conductor 29, back to the negative side of the line. lThemotor will now start with the resistanceR in circuit and as thearmature reaches a predetermined speed the counter electromotive forcerelay E will operate to short circuit the resistance R and bring themotor up to running. speed. If now the switch S is moved into engagementwith contact 11 to reverse the motor the switch C will immediately open.When the masterswitch leaves the contact 10, switch C opens and adynamicbrakingcircuit will be closed from the armature A, through theconductor 27, winding 15 contacts 23 on the switch D, conductor 28,brake resistance BR, contacts 19, and windln -14 of the switch n C tothe opposite side o the armature. It

will benot that the windings 14 and 15 of the switches C and D areenergized by this dynamic braking current `so as vto rmly hold theswitches in their open or dynamic brak- What I claim as new ingposition. The winding 15 preventsthe switch D from closing when themaster switch is moved on to contact 11, and will not permit it to closeuntil the current in the winding 15 decreases practically to zero by thearmature being brought substantially to rest. The dynamic braking actionn'owtakes place through the resistance BR and the armature is graduallyslowed down. When the armature reaches a predetermined speed at which itis safe to increase the dynamic braking current, the relay E will dropso as to short circuit the resistance BR, thereby increasing the brakingcurrent and bringing the motor to rest. As soon as the armature has beenbrought to rest or substantially so, the energizing winding 13 willclose the switch D so as to reverse the current through the motorarmature. The current through the armature will now be from the positiveside of the line through the resistanceR, contacts 22, winding 15,conductor 27, armature A, winding 14,. and contacts 19 of switch C,thence through conductor 29 to the negative side of the line. When themotor reaches a predetermined speed the counter electromotive forcerelay will lagain operate to short circuit the resistance R. When themaster switch S is moved out of engagement with contact 11 the motorwill be dynamically braked through the resistance BR and after the motorhas been slowed down to a predetermined speed the relay will drop toshort circuit the resistance BR and the n10-- tor will bebrought torest. It will be seen that by this arran ement a single relay .I do notlimit my invention thereto, since various modic'ations thereof will .sugest themselves to those skilled in the art without departing from thespirit of my invention, the scope of which is set forth in the annexedclaims.

and desire to secure by Letters Patent of the United States, is:

counterielectromotive force relay controlled by the motor, andconnections whereby said relay automatlcally operates to shortV circuitsaid resistance as the motor speeds up and dynamically brake the motoras the latter slows down.

3. The combination with an electric motor and a starting resistancetherefor, of a dy- .namicbrakinglesistanca a relay controlled by themotor ving two positions, and connections whereby said relay shortcircuits the starting resistance in one position and short circults thebraking resistance 'in the other position.

4. The combination with an electric motor and a starting resistancetherefor, of a dy- ,v

Y namic braking resistance, a relay controlled by the motor, andconnections whereby said relay short circuits the starting resistance asthe motor speeds up and short circuits the braking resistance as themotorslows down.

5. The combination with an electric motor and a starting resistancetherefor, of a dynamic braking resistance, a. counter electromotiveforce relay, and connections whereby said relay short circuits thestarting resistance as the motor speeds up and short circuits thebraking resistance as the motor slows down.

6. The combination with an electric motor, and a starting resistancethereof, of a dynamic braking resistance, a counter elec-v tromotiveforce relay' having two ositions, and connections whereby said re ayshort circuits the starting resistance in one pcsltion and shortcircuits the braking resistance in the other position.

I 7. The combination with an electric motor, of'a starting resistancetherefor, a pair of electromagnetic switches one for closing 'the'motorcircuit through said resistance for each' direction of rotation, adynamic braking resistance, connections whereby the` motor armature isshort circuited throu h said vbraking resistance when both of saldswitches are open, a counter electromotive force relay, and connectionswhereby said relay short circuits the starting resistance as'the motorspeeds up and short circuits the braking resistance as the motor slowsdown.

8. The combination with an electric motor, of a startin resistancethereof, reversing mechanism or closin the motor circuit through saidresistance or each direction of rotation, a dynamic braking resistance,

connections whereby the motor armature isl short circuited through saidbraking resistance, a counter electromotive force relay,

and connections whereby said Vrelay short circuits the startingresistance assthe` motor speeds up in either direction and short cir.-vcuits the braking resistance as the motor slows down.

In witness whereof, I have hereunto set my hand this 29th day of July,1912.

i GEORGE E.\ STACK.

Witnesses:

BENJAMIN B. HULL, HnmN Oaronn. l,

